As is known, the manufacturing process of titanium bioxide via sulfate involves a first step of attack of ilmenite with sulfuric acid, followed by a hydrolysis step that leads to said titanium bioxide which is a pigment with important industrial uses. The effluent coming from the hydrolysis step is subjected to a process of crystallization from which the so-called "copperas" or heptahydrated iron sulfate results with agricultural uses and that is used to manufacture mixed feeds and that, in ferric sulfate form is used to treat water.
The crystallization water is concentrated and afterwards filtered, recycling the filtrate in the first attack step with sulfuric acid.
The residue of filtration is a metal sulfate mixture that cannot be stored as waste material due to leaching problems, whose only use developed up to now has been the production of sulfuric acid by means of roasting, which involves costly investments.
Afterwards some patents which describe the use of this by-product in the manufacture of sulfuric acid are indicated:
Bayer's European patent "A" which refers to the use of a Fundabac filter for the separation of salts. PA1 Bayer's European patent "B" which refers to a process to elaborate sulfuric acids which contain metal sulfate, called "fine acids," by means of concentration by evaporation. PA1 Bayer's European patent 139120 "B" which refers to the production of sulfur dioxide by thermal decomposition of metal sulfates and simultaneous roasting of sulfide ores. PA1 Bayer's European patent 145984 "A", which refers to a sulfate process in which the residual acid and the metal sulfates are recycled, at least in part, at the digestion step. PA1 Bayer's European patent 0194544 "A" which refers to a process for recirculation of sulfuric acid used containing metal sulfates, by means of evaporation until a concentration of 40-85% of H.sub.2 SO.sub.4.
The basic advantage that the present invention provides over the present prior art is that it makes it possible to transform the cited by-product into a marketable product by means of a simple process in a low cost installation.